1. Field of the Invention
This invention is directed to method and apparatus for placing water-soluble polymers and other chemicals into water to produce optimum properties of the solution and to obtain data to facilitate the process. More particularly, a portable tube bundle containing static mixers for effective blending without excessive shearing or damage to the polymer and chemical transport and storage apparatus with sensors and a programmable chemical delivery system are provided.
2. Description of Related Art
One purpose of a blending or mixing system as disclosed herein is to allow a water-soluble polymer and other chemicals to be blended from a dispersion in oil into water or an aqueous liquid and to obtain maximum benefits of the polymer. Such a device is commonly called a blending system when used in conjunction with the fluids used in oil and gas wells. It may be used in any application where there is a need to mix polymer or other chemicals in a continuous and a controlled manner. To insure the effective and even distribution of the polymer or other chemicals into the water, the polymer must be wet by the water and thoroughly dispersed such that the polymer does not form clusters or aggregates, often called “fisheyes.” The polymer normally requires sufficient agitation and retention time as to allow the polymer chains to unfold, causing the polymer solution to reach its maximum dispersion. With batch mixing, this retention time is accomplished by the use of tanks that have a large enough capacity to allow the mixture proper retention time prior to use. Normally, this is performed through the use of two or more compartmented tanks that allow mixing to occur in one or more tanks while the fluid that has already been mixed in the other tank or tanks is pumped. The size of the tanks used for this type of batch mixing is dependent on the rate that the fluid is being pumped from the system and the total mixing time required for the chemicals being used, but the tanks are expensive to transport and they form a large footprint. One of the major limitations to batch mixing is that conditions may change and a batch may not be needed for pumping into a well. This creates the problem of disposing of the mixed solution.
The amount of fluid used in many oil and gas well completion operations has increased in size. In horizontal wells, higher pump rates generally must be used to perform flow or circulation within the wellbore during completion operations, such as drilling out plugs and removing solids. The polymers that are introduced into the fluid medium help not only to transport the particles but also to reduce the frictional pressure loss as fluid is pumped at higher rates through tubulars in the well bore. It is important that the polymers and any other chemicals added to the fluid be introduced in a controlled operation. Preferably, the composition and properties of the fluid mixed and pumped should be measured and the data preserved, along with additional information on water quality, temperature, viscosity, and density.
Injection rates used in hydraulic fracturing operations have also increased in recent years. Polymer is added to the fluids to decrease friction pressure drop as the fracturing fluid (called “slick water”) is injected. Other types of polymers may be used to help suspend proppant in the fluid. In many cases the polymers being used do not have sufficient contact and mixing time prior to being pumped into the wellbore to completely hydrate, thereby limiting the effectiveness of the polymers. This may require overdosing of chemicals to achieve the desired results.
In some cases larger tanks with recirculation pumps have been incorporated into the completion and fracturing operations in an effort to improve the mixing and retention time of polymers. However, the recirculation pumps may lead to excessive shear of polymers, which can break the long chains of the polymers that are being mixed, resulting in lower effectiveness of the polymer solution.
U.S. Pat. No. 7,048,432 discloses a method and apparatus for hydrating a polymer for use in wells. The polymer solution is directed through a housing containing rotating impellers. U.S. Pat No. 4,828,034 discloses mixing a polymer into an oil-based fluid to form an oil-based polymer concentrate, then injecting the oil-based slurry into a water stream and pumping the mixture through a high-shear pump and a static mixer into a first holding tank, then pumping the liquid through a second high-shear pump into a second holding tank. U.S. Pat No. 4,336,345 discloses formation of a polymer concentrate containing an inhibitor to hydration, then reversing the inhibitor reaction to allow full hydration of the polymer.
What is needed is a blending system that overcomes the lack of retention time, excess shearing of the solution, the complexity of batch and continuous operations disclosed above and that can maintain a steady pump and mixing rate at an economical cost.